1. Field of the Invention
The present invention relates to a motor, and more particularly, to a method and an apparatus for driving a polyphase sensorless motor using a driving-current application initial position and a driving-current application period which is detected based on an inductance variation of a plurality of phase coils.
2. Description of the Prior Art
In general, a video cassette recorder includes a capstan motor and a head drum motor. A prior video cassette recorder determines a position of a rotor for driving the motors by using sensors, such as a hole sensor or an optical sensor, and controls a commutation of a phase current which is applied to the motors according to the determined position information.
However, in the sensor-type, a space for installing the sensors is required and the cost of a product is increased by using expensive sensors.
Accordingly, a sensorless-type which does not use the sensors is currently widely adopted.
For example, U.S. Pat. No. 5,235,264 (granted to Isao Kaneda et al.) titled "METHOD OF AND CIRCUIT FOR STARTING SENSORLESS MOTOR" discloses a method and a circuit for detecting a back electromotive force which is inducted to a phase coil in order to determine the position of the magnetic rotor of the sensorless motor and for determining the commutation of the magnetic rotor based on the detected back electromotive force.
A strength of the back electromotive force which is inducted to a coil is proportioned to a rotation speed of the rotor. Therefore, in a back electromotive force-type, when a driving status of the rotor is either a stop status or a low speed status, the back electromotive force does not exist or is very small. As a result, in the back electromotive force-type, a control of the commutation is not accurate before the rotor is rotated more than a predetermined speed which the back electromotive force being detected sufficiently.